1. Field of the Invention
The present invention relates to a pneumatic tire, and, more particularly, to a pneumatic tire capable of suppressing a crack at the bottom of a groove.
2. Description of the Related Art
During driving of a vehicle with conventional pneumatic tires, a rib is deformed caused by a load that is applied from a road to a tread surface of the pneumatic tire, and grooves formed on the tread surface are also deformed caused by the rib deformed. Particularly, the load is easily applied to a shoulder rib that is formed at an edge of a shoulder portion side during the driving of the vehicle, and a groove near the shoulder rib is largely deformed. Therefore, a crack may occur in the bottom of the groove in this portion. In some of the conventional pneumatic tires, the strength of the groove situated at the edge of the shoulder portion side and of the periphery of the groove is improved.
This type of pneumatic tire is disclosed, for example, in Japanese Patent Application Laid-Open No. 2001-63315. In this pneumatic tire, at least one circumferential belt layer is arranged at an inner side of the groove situated at the edge of the shoulder portion, side in a tire radial direction, and a projection is provided in the bottom of the groove. This configuration causes the groove to be reinforced and occurrence of a crack in the bottom of the groove to be reduced. Another example of the same type of pneumatic tire is disclosed in Japanese Patent Application Laid-Open No. 2001-213115. In this pneumatic tire, a circumferential belt layer and an auxiliary belt layer made of organic fabric code are provided at an inner side of the groove of the shoulder portion side in the tire radial direction. With this configuration, the periphery of the groove at the edge of the shoulder portion side is reinforced, which allows reduction of a crack in the bottom of the groove.
If a projection is provided in the groove, however, the capacity of a space in the groove is reduced, which may cause drainage to be reduced when a vehicle is driven in the rain. Furthermore, when a predetermined groove width is ensured to increase the drainage and the inner side in the tire radial direction of the groove is reinforced by the circumferential belt layer and the auxiliary belt layer, a pebble or so is caught in the groove and a part of the groove may be chipped. In such cases, it is difficult to ensure compatibility between suppression of the crack in the bottom of the groove and some other performances.